Abstract: In an aging device used to manufacture a plastic molded product, injecting and aging processes are separated from each other. Namely, a plastic base material is approximately processed in advance in a final shape by injection molding. Thereafter, the plastic base material is inserted into an aging die having plural cavities and attached to a press machine such that the aging die is clamped and opened. Next, the plastic base material is heated and melted until a temperature equal to or higher than a glass transition point so as to generate an internal resin pressure. Next, the plastic base material is gradually cooled to transfer a mirror face thereto. The aging device has a die cooling device having plural heat pipes for cooling the die and has a die heating device having plural heaters for heating the die. The heat pipes and the heaters are arranged in a die plate of the press machine.